This research encompasses studies of a pineal antigonadotropic substance having peptidic characteristics. The overall objective is to further characterize the biological response to the pineal antigonadotropin and study the efficacy of the purified material as an antifertility agent. The material is prepared by acetic acid extraction of bovine pineal glands and further purified by gel-filtration and electrophoresis. The identity and activity of the material is determined by its ability to inhibit compensatory ovarian hypertrophy and the post-castration rise of LH in male rats. The antigonadotropin is used in three experimental models to determine its efficacy on the inhibition of ovulation, implantation and term pregnancy in rats. Where results are positive, the alteration of blood levels of LH, prolactin, 17 beta estradiol estrone and progesterone will be determined.